The invention relates to an adjusting device for a pneumatically actuated disk brake.
A first adjusting device is known from German patent publication DE 40 34 165, reference being made to the full contents of this document. In particular, the adjusting device of the invention is likewise suitable for a disk brake which is actuated by compressed air, in particular in a sliding caliper design, as is shown in this document. Moreover, they can also be used, however, in fixed caliper or pivoting caliper disk brakes which are actuated by compressed air.
Pneumatically actuated disk brakes of this type now belong to the standard equipment of heavy commercial vehicles, where they replace the previously customary drum brakes more and more.
Disk brakes of this type require a mechanical transmission means in order to generate the required brake application of force, as the force of the pneumatically loaded brake cylinders is limited on account of the pressure level (currently approximately 10 bar) and the limited overall size of the brake cylinders. In the pneumatically actuated disk brakes which are known at present, transmission ratios are found between 10:1 and 20:1 which are realized by means of an eccentrically mounted rotary lever in the generic prior art.
The piston strokes of the brake cylinders are between 50 and 75 mm, and this results in brake application paths for pressing the brake linings against the brake disk of approximately 4 mm.
The friction material thickness of the brake linings lies in the region of 20 mm. As two linings are installed, the result is therefore a wear travel of approximately 40 mm, without taking the disk wear into consideration. This travel is greater by a multiple than the abovementioned brake application travel. There is therefore necessity to adjust the brake by means of a device, in a manner which corresponds to the lining wear.
German patent publication DE 40 34 165 A1 achieves this by means of an automatically operating wear adjusting means having a freewheel and an overload coupling (see, for example, FIG. 5 of that document). This achieves a situation where what is known as the air play (this means the gap between the brake linings and the brake disk in the non-actuated state) is kept constant independently of the wear state and wear behavior of the brake linings.
Furthermore, the DE 40 34 165 A1 publication proposes to arrange the adjusting device concentrically in the hollow space of a threaded ram (a threaded spindle) and to drive it from the brake lever eccentrically via a drive element (switching finger).
During braking, the brake lever which is coupled to the piston rod of the brake cylinder performs a rotary movement. Before the rotary movement of the rotary lever is introduced into the adjusting device via the coupling mechanism of the adjusting means (for example, switching fork and switching finger), what is known as an idle travel has to be overcome. This travel is critical for the magnitude of the air play, as the adjusting means is not activated during this movement and the travel of the pressure pistons therefore represents the air play. After this idle travel is overcome, the adjusting device is set into a rotary movement and an adjusting process is initiated by the coupling to the threaded tube.
However, this is only the case when the air play is too great. If the air play has the correct size, the brake linings come into contact with the brake disk at the same time as the switching fingers come into contact with the switching fork of the adjusting device, and a rotation of the threaded tube is no longer possible on account of the high frictional force which is caused by this in the thread.
Nevertheless, the brake lever is rotated further, as a result of the deformation of the component (linings, caliper, mechanical means) which is situated in the force flow, and a rotary movement is also initiated at the adjusting device, furthermore, on account of the direct coupling of the switching fork to the brake lever.
In order that the adjusting device is not damaged, it has to be equipped with what is known as the overload coupling. In the case of the generic prior art (FIG. 5 of the generic document), this is ensured by a ball ramp coupling which unlatches if a defined torque is exceeded.
A further basic component of the adjusting device is the directional coupling, what is known as a clamping roller freewheel in the case of the adjusting device which is described in the above text. This freewheel achieves a situation where the adjusting device can be rotated by the brake lever only in the brake application direction.
During a lining change, the wear adjusting means has to be rotated back into the initial position again. During resetting, the adjusting device has to be rotated counter to the locking direction of the freewheel, which is made possible by the overload coupling which unlatches at a defined torque. An unlimited return rotational angle is possible as a result of the “overrolling function”.
In addition to other components, the adjusting device which has been described in the above text therefore necessarily has a clamping roller freewheel and an overload coupling. In order to function reliably, the clamping roller freewheel requires a very accurately manufactured mating running face and a precisely manufactured press fit.
It has therefore been proposed in generic German patent document DE 197 29 024 C1 to combine the unidirectional rotational coupling and the overload coupling to form a combined unidirectional rotary and overload coupling system. Nevertheless, there is also a requirement for a further reduction in the manufacturing costs of this solution.
Against this background, it is the object of the invention to develop the generic adjusting device in such a way that it can be manufactured with as few components as possible and inexpensively with a low processing expenditure. In addition, optimization of the function and service life is preferably also aimed for.
A basic principle of the adjusting device is again a combination of the freewheel and the overload coupling in one functional unit which is configured here, however, to be particularly inexpensive, robust and functionally reliable, in particular by means of a conical seat as an inexpensive failsafe functional element.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.